This invention relates to a device for detecting relative humidity.
Devices for the detection of atmospheric conditions are legion. In particular, devices for the detection of relative humidity are known; such devices are often called humidistats.
One known type of humidistat uses an element having at least a portion movable in response to a sensed humidity. Often, the movement is a change in a physical dimension of the element. For example, human hair is often used as the humidity sensing element. The hair is placed under longitudinal tension by a biasing load. As the ambient humidity changes, the hair changes in length.
However, the change in length of a hair element usually is relatively small per unit length of the hair. Typical humidity responsive changes in length of such hair elements are in a range of 2%. Normally, hair movement is converted to an electrical output signal indicating humidity by means of a rheostat which has inherent friction.
It is desirable to provide constant load biasing the hair with minimal friction against hair movement over the entire range of the humidity sensing element.